Troubleshooting ignition coil issue...

[Jason280]

In my ongoing saga with a Stihl 066 Magnum...

http://www.arboristsite.com/community/threads/stihl-066-magnum.263527/

http://www.arboristsite.com/community/threads/ok-ive-been-defeated.263994/

...I've now run into a "no crank" issue. I completely rebuilt the carb, installed new impulse line, fuel hose, and filter, and now can't get the saw to crank. I pulled out my multimeter, and found I am getting continuity across the green/yellow and black wires below the carb, regardless of the switch position. Traced the wires back to the ignition coil/module, and found I was getting continuity there as well. Thinking I likely had a fray between the wires, I went ahead and pulled the module and disconnected the wires...still getting continuity across the module (wiring is actually OK).





If you will look at the pic above with the two red boxes, I am getting continuity between those two points (where the green/yellow and black wires attach to the module). I compared this with my Stihl 026, and do not get continuity across those wires. If I understand this purpose of these two wires, they simply "ground out" to cut the coil off (for lack of a better word) when the switch is OFF, so it would appear I am simply getting no spark to the plug (hence, the no start).

I'm assuming the coil has gone bad, but I am not sure. The coil/ignition was working fine prior to the rebuild, and it was not touched while I was working on the saw, so I have no idea why the sudden problem. Is it common for these modules to suddenly die, or am I likely looking at a different problem altogether?

This endeavor has become certainly more frustrating, as it doesn't look like ignition modules are cheap....its just very odd that it would suddenly start having issues, especially considering all I have done is replace fuel components.

 

[Welder56]

If you go to the 20k ohms on the multimeter. Put red lead into the plug boot (onto the spring) and black to a ground. Should read 8k-12k for normal reading. If it doesn't read anything pull the spark plug wire out of coil and check inside the coil (same test, should be a little spike in there). If that reads good it could be a break in your HT lead (spark plug wire) or your spring that connects to the wire is broken or not connected properly to the wire

 

[particleperson]

I measure conductive between those boxed terminals on both a new chinese 026 coil, and also my present 026 coil. On your 026 terminals, get the probe contact points shiny first, and check again.

I measure 8 kohm on the plug wire to ground as Welder56 says.

 

[Jason280]

Ok, did a few measurements with the multimeter set to resistance. Spade terminal (black wire to the module) to ground ranges from 0.7-1.1, with high being 1.3-1.4 ohms. Common ground (cooling fins on head) to plug boot ranges 12.88k-12.91k ohms. I reset my gap to 0.008", and I am actually getting spark now to the plug. I can switch the saw to "OFF", and lose spark, so looks like the switching is OK (still have spark outside of the head with the switch "ON"). I haven't been able to get the saw to fire on starter fluid, though, and haven't tried it on fuel from the tank. I'm running a Champion CJ8 plug gapped to 0.035, but it looks that needs to be closed to 0.020". I may even need to replace the plug altogether....

 

[Welder56]

Well that's great news for your ignition system everything sounds perfect. Every new plug you buy you should set the gap. Have you vacuum / pressure tested to see if there's an air leak?

 

[Jason280]

Haven't done any type of pressure test, other than compression in the cylinder (150 psi). Not sure I have a vacuum set up that will pull enough, have to check in the shop....I know I have a Mity-Vac brake bleeder kit that may work. Where do I need to try and pull vacuum from?

 

[Jason280]

Looking at the charts, its possible the wrong plug was in the saw. It had a CJ8 when I picked up the saw, but looks like it actually calls for a CJ6Y. Not sure how much difference would be between the plugs. but I'll pick up a replacement and go from there.

 

[Jason280]

This saw continues to be a pain in my *ss, and it makes no sense....I have covered all the basics. I would be happy if it would have simply returned to its previous condition of no idle, but I keep fighting this no crank that's absolutely brand new since the carb was rebuilt. This condition simply did not exist until I started working on the carb, and its odd because the ignition module was not touched during any of this. It cranked without issue before, just wouldn't idle correctly.

Here's what I have done so far:
-Rebuilt carb with Stihl rebuild kit
-Changed plug to NGK, gapped 0.020
-New fuel filter, fuel line in tank, and impulse hose
-Flywheel cleaned, ignition module gapped to 0.008"
-Checked compression, 150 psi

I have checked spark, and I am getting a good/blue spark with the plug grounded to the cylinder head. However, once the plug is installed, everything shuts down. I can't get it to fire with gas in the tank, I can't get it to fire by spraying starter fluid though the carb, and I can't get it to fire spraying starter fluid straight into the cylinder head. I've pulled the carb off a couple times, and I am getting fuel to the carb itself.

Now, I did disassemble the carb a couple times to make sure the gaskets were correct, and I was able to get a quick "pop" trying to crank the saw. It would fire for maybe a revolution or two on choke, then fire again on fast idle for maybe a brief half-second, enough to reset the decompression valve. But that's it, nothing more. It has to be something simple, I'm just not seeing it.

Here are a few random pics of the carb:





Also, just to confirm a few things:



In the pic above, there are three gaskets on the bottom of the carb. Two are black, one is transparent. Just to make sure, the order these are assembled are from right to left facing to the bottom of the carb, with the transparent gasket being against the bottom face of the carburetor.

 

[AKDoug]

You only use one of those two left gaskets... use either the black or the transparent. I haven't had an 066 apart in a while, but I think it used the transparent one.

 

[AKDoug]

Remember, on the other side it's gasket against the carb, diaphragm above that, then the cover.

 

[Jason280]

I know when I rebuilt the carb, it had a transparent gasket, so I'll just run it with the other gasket (leave the middle one out).

 

[DSS]

It almost certainly hooked a ring in the port. Looks like the piston was put in backwards.

If the nikasil is scored in your cylinder, its junk. If it just has aluminum transfer, it can be cleaned. It can't be honed or bored oversize.

 

[Little Al]

This saw continues to be a pain in my *ss, and it makes no sense....I have covered all the basics. I would be happy if it would have simply returned to its previous condition of no idle, but I keep fighting this no crank that's absolutely brand new since the carb was rebuilt. This condition simply did not exist until I started working on the carb, and its odd because the ignition module was not touched during any of this. It cranked without issue before, just wouldn't idle correctly.

Here's what I have done so far:
-Rebuilt carb with Stihl rebuild kit
-Changed plug to NGK, gapped 0.020
-New fuel filter, fuel line in tank, and impulse hose
-Flywheel cleaned, ignition module gapped to 0.008"
-Checked compression, 150 psi

I have checked spark, and I am getting a good/blue spark with the plug grounded to the cylinder head. However, once the plug is installed, everything shuts down. I can't get it to fire with gas in the tank, I can't get it to fire by spraying starter fluid though the carb, and I can't get it to fire spraying starter fluid straight into the cylinder head. I've pulled the carb off a couple times, and I am getting fuel to the carb itself.

Now, I did disassemble the carb a couple times to make sure the gaskets were correct, and I was able to get a quick "pop" trying to crank the saw. It would fire for maybe a revolution or two on choke, then fire again on fast idle for maybe a brief half-second, enough to reset the decompression valve. But that's it, nothing more. It has to be something simple, I'm just not seeing it.

Here are a few random pics of the carb:





Also, just to confirm a few things:



In the pic above, there are three gaskets on the bottom of the carb. Two are black, one is transparent. Just to make sure, the order these are assembled are from right to left facing to the bottom of the carb, with the transparent gasket being against the bottom face of the carburetor.

You only use either the top left or top centre pump diaphragm, next to the carb body then the gasket top right then carb pump cover, the translucent diaphragm is for fuel containing ethanol, the black one is for ethanol free fuel

 

[Jason280]

Interesting, I never knew that.

 

[Jason280]

It almost certainly hooked a ring in the port. Looks like the piston was put in backwards.

If the nikasil is scored in your cylinder, its junk. If it just has aluminum transfer, it can be cleaned. It can't be honed or bored oversize.

???

 

[Wood Doctor]

I know guys like to tinker with carburetors and carb rebuild kits, but you have to wonder if it's really worth it. New carbs run less than $30 these days and sometimes less than $20. I have yet to buy a replacement carb that failed whenever that was indeed the problem.

 

[struggle]

IF the saw is still in a no run state? I have a question did you pressure/vac test the saw and now it won't start after that? Did you leave a block off rubber behind the exhaust or intake?

Don't ask me how I know this

 

[Jason280]

No, the saw hasn't been pressure or vacuum tested. I wish it was something simple like that, though!

I'm going to start back from square one this weekend, and go through all the basics again. I have a sneaking suspicion that I am somehow losing spark in the cylinder, but not sure why considering I have such a strong spark outside of the cylinder.

Just to confirm, is the spec gap for the flywheel to ignition module supposed to be .008"?

 

[AKDoug]

.008" is fine. I really think it isn't an ignition problem. With a no idle the FIRST place I look is crankcase leaks.

 

[jwilly]

Try switching to a real spark plug. I had a new Champion that would spark great outside the saw but once installed, nothing. Grabbed an old Bosch from the tool box and saw ran fine.